Low noise amplifiers (LNAs) are the building blocks of any communication system. For example, a low-noise amplifier is typically the first active circuit after the antenna in a radio transceiver, and is thus a critical building block for a radio transceiver. To increase receiver sensitivity and reduce the amount of noise contributed by subsequent stages, the LNA is required to have a moderate gain and a low-noise figure. The LNA is required to be matched to the characteristic impedance of the system (usually 50 ohms) at its input and output. In addition, to operate at millimeter-wave (mm-wave) frequencies (30 GHz and higher), such systems must often be capable of transmitting, receiving and manipulating mm-wave signals.
As MOSFET miniaturization reaches deep submicron sizes (0.5 mm and below), mm-wave LNAs and other amplifiers require multi-stage designs to achieve the necessary gain. Due to process variations, model inaccuracies and the extra parasitics related to wiring, however, the various stages will typically operate at different frequencies. As a result, the total gain decreases and the bandwidth of the amplifier will change. In addition, the frequency response of the amplifier (S21) exhibits a frequency shift and the input/output matching will be impaired. For lower frequencies, such as microwave frequencies, tunable varactors can be used. A varactor has a capacitance that varies with the applied voltage. At mm-wave frequencies, however, varactors have a low quality factor. Therefore, varactors cannot be used at mm-wave frequencies for varying the capacitance.
U.S. patent application Ser. No. 13/251256, filed 2 Oct. 2011, entitled “Structure and Modeling of Variable Transmission Lines,” discloses a tunable transmission line that is digitally tuned to compensate for process variations in both the active and passive devices of the RF design. A disclosed variable transmission line comprises a semiconductor substrate, a signal line, a first plurality of capacitor ports below the signal line, where each capacitor port is operative to be connected to either ground or a floating potential, a bottom ground plane and one or more side shield wires.
A need remains for a digitally controlled resonator for resonant amplifiers based on a tunable passive component. A further need exists for a multi-stage digitally controlled resonator for resonant amplifiers where the amplification stages are identical and working at the same resonant frequency that can be controlled in a digital manner. Yet another need exists for a method to employ the resonator in the digital calibration of the frequency response of the amplifiers.